The present invention relates generally to fluid valves, and more particularly to a micro-valve that utilizes electrostatic forces to form a viscoelastic material disposed in the passageway of a valve body to modulate a fluid flow.
Various types of micro-valves are known for modulating a flow of fluid. Such valves find particular use in such fields as analytical chemistry wherein an accurate and measured control of a very small liquid sample is required. Such valves also find application in printers, wherein a precise and rapid control of a flow of a dye, ink, or other image creating liquid is necessary.
Many prior art micro-valves utilize electromechanical mechanisms which while effective are relatively complex and expensive to manufacture on the small scales necessary to modulate small fluid flows. For example, micro-valves utilizing piezoelectric materials are known wherein a valve element is moved into a fluid obstructing or fluid conducting position by the application of electrical impulses on piezoelectric crystals. Unfortunately, piezoelectric crystals are formed from brittle, ceramic materials which are difficult and expensive to machine, particularly on small scales. Additionally, piezoelectric materials generally are not suitable for interfacing with fluids. Thus, valves that exploit piezoelectric movement must be designed to insulate the piezoelectric crystals from contact with liquid materials. Finally, piezoelectric materials generally cannot be fabricated by way of known CMOS processes. Hence, while the electrical circuitry necessary to drive and control piezoelectric movement within a micro-valve may be easily and cheaply manufactured by CMOS processes, the integration of the piezoelectric materials and such circuits requires relatively specialized and slow fabrication steps.
Clearly, there is a need for a micro-valve which is capable of accurately and rapidly modulating a fluid flow without the need for relatively expensive and difficult to machine materials. Ideally, all of the components of such a micro-valve could be manufactured from relatively inexpensive, easily worked with materials which are compatible both with contact with liquids and with CMOS manufacturing techniques.
Generally speaking, the invention is an electrostrictive micro-valve for modulating a fluid flow that overcomes or at least ameliorates all of the aforementioned shortcomings associated with the prior art. The micro-valve of the invention generally comprises a valve body having a passageway for conducting a flow of fluid, a valve element formed from a piece of viscoelastic material and disposed in said passageway, and a control assembly coupled to the viscoelastic material for electrostatically controlling the shape of the viscoelastic material to open or close the passageway.
The control assembly may include a pair of electrodes disposed on opposite sides of the viscoelastic material. In one embodiment of the invention, the control assembly includes a source of electrical voltage connected across the pair of electrodes, and a switching circuit for selectively applying a voltage from the source across the electrodes to generate an electrostatic force therebetween. One of the electrodes is a flexible, electrically conducting coating disposed over an upper, fluid contacting side of the viscoelastic material, while the other electrode is a plurality of interconnected panels for providing a charge pattern on the other side of the viscoelastic material when the voltage source is connected across the electrodes. The patterned shape of the lower electrode results in localized electrostatic forces across the viscoelastic material that in turn generates a sinusoidal ripple throughout the material whose peak portions act as obstructions throughout the valve body that partially or completely obstruct a fluid flow.
In another embodiment of the invention, the bottom electrode is formed from a layer of photoconductive material which is covered on one surface with a patterned, light-obstructing mask. The control assembly continuously applies a biasing voltage across the upper and lower electrodes. When light is admitted through the openings in the mask, an electrostatic charge pattern is generated between the two electrodes which again results in a sinusoidal ripple pattern in the viscoelastic material that forms the valve element.
The electrostrictive micro-valve of the invention is fabricated from relatively inexpensive and easily worked with materials, and the electrode structure of the control assembly may be easily manufactured by CMOS technology. The inherent elastic properties of commercially available viscoelastic materials advantageously allow the micro-valve of the invention to be operated at frequencies as high as 12.5 kHz.